1. Field of the Invention
The present invention relates to a commutator, a manufacturing method of the commutator, a manufacturing apparatus of the commutator and a commutator plate material.
2. Description of Related Art
A previously proposed commutator includes a generally cylindrical dielectric body and a plurality of commutator segments. The dielectric body is made of a resin material, and the commutator segments are arranged along an outer peripheral surface of the dielectric body in the circumferential direction of the dielectric body. Such a commutator is formed in the following manner. That is, a commutator plate material is rolled into a cylindrical shape. Then, a resin material in a liquid state is filled into an inner space of the cylindrically rolled plate material. After solidification of the resin material, the cylindrically rolled plate material is cut and is divided into a plurality of segments at generally equal angular intervals. Each divided segment forms the commutator segment, and the solidified resin material forms the dielectric body.
In the above commutator plate material, a plurality of ridges is formed in such a manner that the ridges extend parallel to one another in a direction that corresponds to the axial direction of the commutator, and the number of the ridges corresponds to the number of the commutator segments (e.g., one ridge per one commutator segment). A plurality of protrusions, which protrude in a direction perpendicular to a projecting direction of the ridge, is provided in each ridge. When the commutator plate material is rolled into the cylindrical shape, the ridges and the protrusions are arranged on the inner peripheral side of the commutator plate material and are engaged with the solidified resin material to prevent detachment of the respective commutator segments from the dielectric body upon cutting of the commutator plate material into the commutator segments.
Such a commutator is disclosed in, for example, Japanese Unexamined Patent Publication No. 2001-245456 that corresponds to U.S. Pat. No. 6,489,703, the contents of which are incorporated by reference.
However, in the above-described commutator, each ridge of the commutator segment extends continuously at a generally constant height (i.e., a generally constant projecting length) from one axial end of the commutator segment main body to the other axial end of the commutator segment main body. Thus, each ridge does not substantially engage with the dielectric body in the axial direction. Because of this, at the time of resistance welding between a commutator riser, which extends from one axial end of the commutator segment main body, and a corresponding coil, a relatively large force is radially inwardly applied from a fusing electrode to the one axial end of the corresponding commutator segment main body through the commutator riser. The application of the relatively large force can cause lifting of the other axial end of the commutator segment main body. This will form steps from one commutator segment to the next commutator segment and will prevent smooth sliding engagement between the commutator segments and power supply brushes upon rotation of the motor. As a result, mechanical vibrations, mechanical noises and electric noises are generated upon rotation of the motor.